Breast cancer (BC) is the most common cancer among women worldwide. American women have a 1 in 8 lifetime probability of developing BC. Nevertheless, death rates from BC have steadily decreased since 1990 and women are surviving longer with the disease. Thus, health care professionals face a new set of challenges beyond decreasing mortality: helping BC patients, survivors, and their family members cope with the cancer experience. The effects of BC diagnosis and treatment occur in an interpersonal context. Recent research has documented that BC diagnosis and treatment affect the patient's spouse/partner as well as the couple's relationship functioning. However, most of this research has involved global, cross-sectional assessments that can obfuscate our understanding of interpersonal processes. In addition, this research has usually relied on retrospective reports by both patients and their spouses/partners. There are several problems with retrospective reports, including systematic recall biases associated with concurrent mood and/or psychological adjustment. To address these problems, and to capture behavior and mood "in the moment," health researchers are beginning to use diary designs to assess the daily functioning of medical patients. None of this research has focused on BC patients and their spouses/ partners in the same study. One likely reason for this is the unknown feasibility of applying a diary methodology to couples coping with cancer. The primary purpose of this project is to evaluate the feasibility of an electronic daily diary methodology for research with BC patients and their spouses/partners. Within a few weeks after surgery, BC patients and their spouses/partners will complete a battery of questionnaires. Then, for 10 consecutive nights, BC patients and their spouses/ partners will complete surveys via personal digital assistants (PDAs) that assess their daily experiences, mood, and social support processes. Feasibility of this electronic diary methodology will be evaluated in terms of the percentage of couples who agree to participate in the study and the percentage of participating couples who complete the PDA-based survey each night. The electronic diary methodology will also be used to test two dyadic hypotheses for couples coping with BC. The first focuses on the effect of perceived and received support on the daily adjustment of BC patients and their spouses/partners. The second focuses on day-to-day transmission of emotion between BC patients and their spouses/partners.